The present invention relates to a method for the preparation of a shaped article of a polyvinyl chloride resin with metallized surface. More particularly, the invention relates to a method for the preparation of a shaped article of a flexible or semi-rigid polyvinyl chloride resin with metallized surface, of which the metallizing layer on the surface has remarkably improved adhesion to the surface of the shaped article as the substrate.
Needless to say, the techniques of metallizing, i.e. the techniques for providing a coating layer of, typically, a metal on the surface of a substrate body, e.g. various shaped articles of synthetic resins, are widely undertaken when electroconductivity, antistatic effect, decorative metallic luster, reflectivity or shielding of light and the like properties are desired on the surface of the synthetic resin shaped articles. Sometimes it is also desired that the synthetic resin shaped articles with metallized surface have flexibility at least to some extent as in the application of the article as a wrapping material and the like. A widely practiced way in such a case is to shape the article as the substrate for metallizing of a flexible or semi-rigid polyvinyl chloride resin from the standpoint of the outstanding inexpensiveness and excellent workability, especially, after metallizing as well as the freely controllable flexibility of the resins in comparison with other kinds of synthetic resins.
Unfortunately, however, shaped articles of a flexible or semi-rigid polyvinyl chloride resin with metallized surface are not free from the most serious problems or defects described below. In the first place, the adhesive bonding strength between the metallizing surface layer and the surface of the shaped article as the substrate is relatively low so that the metallizing layer is readily peeled off from the substrate surface even by gentle rubbing. This disadvantage is due not only to the inherently low affinity between the metallizing layer and the polyvinyl chloride resin but also to the bleeding of the plasticizer or other additives always formulated in the flexible or semi-rigid polyvinyl chloride resins on to the surface of the shaped article badly affecting the adhesion as a matter of course. In the second place, the chemical stability and mechanical strengths of the metallizing layer per se are relatively low on the surface of the flexible or semi-rigid polyvinyl chloride resin in comparison with the metallizing layers on other types of synthetic resins. This problem is presumably due to the fact that, assuming that the metallizing is performed by the technique of vacuum vapor deposition, the deposition of the molecules or ions in the metal vapor on to the substrate surface proceeds necessarily in the presence of the plasticizer or other low molecular-weight additives in the atmosphere evaporated from the shaped article due to the vapor pressure thereof not negligibly low so that the metallizing layer is always contaminated by the concurrent deposition of the vapor of these additives with the metal vapor leading to the unavoidable decrease in the chemical stability and mechanical strengths of the metallizing layer. These problems are characteristic in the flexible and semi-rigid polyvinyl chloride resins and out of the question in most of other synthetic resins including rigid polyvinyl chloride resins.
It may be the most easy idea in order to improve the adhesive bonding strength between a substrate surface and a coating layer thereon that the surface is treated in advance with a primer before providing the coating layer. This method of surface priming with certain primers such as a specific organosilane compound is indeed effective to some extent when the synthetic resin of which the article to be metallized is shaped is a polyimide resin or a polyethylene terephthalate resin. Further, several other methods have been proposed for the purpose including the chemical treatment of the substrate surface with a reactive chemical or a solvent, flame treatment, treatment by corona discharge, treatment by sputtering-etching and the like.
These methods hitherto proposed and considerably effective for other synthetic resins are, however, little or not effective when the shaped article is made of a flexible or semi-rigid polyvinyl chloride resin. For example, the adhesion of the above mentioned organosilane compound as a primer to the surface of the flexible or semi-rigid polyvinyl chloride resin is extremely weak so that substantially no improvement can be expected by the priming treatment in the adhesive bonding strength between the metallizing layer and the substrate surface even by setting aside the problems that the adhesion between the primer layer and the metallizing layer is also not sufficiently good and the mechanical strengths of the primer layer per se is also poor.